In This Edition

Unexpected Microbe Diversity on Human Skin

A new study of the skin's microbiome—all of the DNA, or
genomes, of all of the microbes that inhabit human skin—reveals
that our skin is home to a much wider array of bacteria than
previously thought. The accomplishment provides a new foundation
for developing strategies to treat and prevent difficult skin
diseases such as eczema, psoriasis, acne and antibiotic-resistant
infections.

The skin is one of the body's first lines of defense against
illness and injury. Its health depends upon the delicate balance
between our own cells and the millions of bacteria and other
one-celled microbes that live on its surface. To better understand
this balance, NIH researchers drew on the power of modern DNA
sequencing technology and computational analysis.

Scientists at NIH's National Human Genome Research Institute
(NHGRI), National Cancer Institute (NCI) and the NIH Clinical
Center took skin samples from 20 sites on the bodies of 10 healthy
volunteers. They extracted DNA from each sample and sequenced
a type of gene that is specific to bacteria, the 16S ribosomal
RNA gene.

The researchers reported in the journal Science on
May 28, 2009, that they identified, classified and compared more
than 112,000 bacterial gene sequences. Previous methods, which
involved growing microbial samples from human skin in the laboratory,
had uncovered a far less diverse collection.

The greatest influence on bacterial populations appears to be
body location. For example, the bacteria that live under your
arms likely are more similar to those under another person's
arm than they are to the bacteria on your own forearm. There
was also considerable variation in the number of bacteria species
at different sites, with the most diversity on the forearm (44
species on average) and the least diversity behind the ear (19
species on average).

In general, dry and moist skin had a broader variety of microbes
than oily skin. Dry areas include the inside surface of the mid-forearm,
the palm of the hand and the buttock. Moist areas include inside
the nose, armpit and side of the groin. Oily sites include beside
the nose, inside the ear and the upper chest and back.

To look for changes over time, the researchers sampled some
volunteers twice, with the samples taken about 4 to 6 months
apart. Most of the resampled volunteers were more like themselves
over time than they were like other volunteers. However, the
stability of the microbial community was dependent on the site
surveyed. The greatest stability was found in samples from inside
the ear and nose. The least stability was found in samples from
behind the knee.

"Our results underscore that skin is home to vibrant communities
of microbial life, which may significantly influence our health," says
Dr. Elizabeth Grice, a postdoctoral fellow at NHGRI and the study's
first author.

This study is among early research laying the groundwork for
NIH's Human Microbiome Project, which aims to characterize human
microbial communities and their role in health and disease. Other
efforts are sampling the microbiomes of the nose, digestive tract,
mouth and vagina.